The present invention relates to a novel method for the formation of a finely patterned photoresist layer on a substrate surface. More particularly, the invention relates to an improvement in a method for finely patterning a photoresist layer formed on a substrate surface with intervention of a film of an organic anti-reflection agent therebetween in a patterning process involving the steps of patternwise exposure of the photoresist layer to actinic rays and development of the patternwise exposed photoresist layer.
Along with the trend in recent years in the technology of semiconductor devices such as ICs and LSIs and liquid crystal display panels which are imparted with more and more increased fineness and a multilayered structure, a difficult problem to be solved in the photolithographic patterning of a photoresist layer is caused by the standing waves due to the exposure light which adversely influence on the quality of patterning. As is widely practiced in the photolithographic technology, this problem due to standing waves can be solved at least partly by interposing a film of an organic anti-reflection agent between the substrate surface and the photoresist layer thereon. It is noted that the thickness of the intermediate anti-reflection film is desired to be decreased smaller and smaller in order to be in compliance with the trend of the photoresist layer toward a smaller and smaller thickness.
An anti-reflection film for such a purpose can be formed on the substrate surface by several different methods including a method disclosed in Japanese Patent Kokai 11-8248 in which a thin carbon film is formed on the substrate surface by vapor deposition and a method disclosed in Japanese Patent Kokai 8-37140 according to which the optical properties of an organic anti-reflection film can be controlled by conducting formation of the organic anti-reflection film under irradiation with ultraviolet light. These prior art methods, however, do not provide a full solution to the problem due to the standing waves, especially, when the thickness of the anti-reflection film is so small as is mentioned above.
The present invention accordingly has an object to provide a photolithographic method for finely patterning a photoresist layer formed on a substrate surface with intervention of an organic anti-reflection film without being affected by the standing waves of the exposure light even when the thickness of the anti-reflection film is very small. It is a very unique and unexpected discovery that this object of the invention can well be accomplished when the anti-reflection film has a specifically controlled refractive index (n) and absorption coefficient (k) to the patterning exposure light by appropriately selecting the types of the anti-reflection compositions and the contents of the components therein.
Thus, the present invention provides an improvement, in the photolithographic patterning process for patterning of a photoresist layer comprising the steps of: forming an anti-reflection coating film of an organic anti-reflection agent comprising a resinous compound, a highly light-absorbing compound and a thermally crosslinkable compound on the surface of a substrate; forming a photoresist layer on the organic anti-reflection film; patternwise exposing the photoresist layer to light; and subjecting the thus patternwise exposed photoresist layer to a development treatment, which comprises controlling the refractive index and absorption coefficient of the anti-reflection coating film in such a way that, in the curve of a graph plotted for the thickness of the anti-reflection coating film taken as the abscissa values and the reflectivity to the exposure light at the interface between the anti-reflection coating film and the photoresist layer taken as the ordinate values, the range of the abscissa value of the thickness of the anti-reflection coating film corresponding to an increment of 0.01 in the ordinate value of the reflectivity on both sides of the minimum point on the curve does not exceed xc2x10.01 xcexcm.
Preferably, the above-mentioned reflectivity at the interface on the minimum point of the curve should not exceed 0.01. In particular, control of the refractive index and absorption coefficient of the anti-reflection coating film are accomplished by selecting the types and contents of the resinous ingredients contained in the anti-reflection coating composition, by selecting the types and contents of the highly light-absorbing compound contained therein and/or by selecting the types and contents of the thermally crosslinkable compound contained therein.